Crusher/classifier devices are commonly used by electricity generating utilities and other companies to pulverize coal for use in tangential spray combustion chambers. Briefly described, a crusher/classifier comprises a rotatable dish or bowl-shaped table onto which lump coal is deposited by gravity feed, and a plurality of crusher wheels which rollingly contact the table to crush the coal into smaller particles. The classifier function is usually of the updraft type and uses air flow to send the fully crushed fine particles toward the combustion chamber while returning incompletely crushed larger particles or chunks back to the crusher for further processing.
In all cases, the crusher rollers are equipped with and/or mounted to a carriage having a spring-type suspension system which can be adjusted to increase or decrease the crusher force. The adjustment feature determines the amount of pre-compression to be applied to the springs in the suspension system and this, in turn, determines the area along the force-displacement curve associated with the springs in which the system operates. In accordance with Hooke's Law, operating farther out along the force-displacement curve increases the force with which the crusher rollers contact the table. As persons knowledgeable with respect to crusher/classifiers will readily understand, the amount of pre-compression must be limited to allow adequate travel in the compression springs to prevent damage to the equipment in the event an uncrushable foreign object, such as a chunk of metal enters the system.
Crusher/pulverizer devices are available from several sources and utilize somewhat different designs, the largest areas of difference occurring in the size, type and location of the crusher roller suspension systems, the manners in which the suspension systems are anchored, and in the manner in which crusher force is adjusted. Two different crusher/classifiers are described in this document. The crusher force adjustment systems can be purely mechanical and manually adjusted or they can incorporate various types of actuators such as hydro-pneumatic devices which facilitate the adjustment process. Once such system incorporating adjusters of this type is disclosed herein.
Despite the fact that the particle size or “fineness” of coal delivered to the combustion chamber spray nozzles is critical to combustion, slag formation and other operational characteristics, I have found that crusher pressure is not carefully monitored or regulated on a day-to-day or hour-by-hour basis. Instead, crushers are adjusted and then turned on to run unmonitored for long periods of time. I have found that the pressure settings tend to vary with time and may result in different settings at the corners of the suspension system. I have also found that, unless an individual is closely monitoring the crusher/classifier operation, the entry of an uncrushable foreign object such as a metal chunk into the system often goes unnoticed. This can result not only in poor pressure/classifier performance until the object is removed but may also result in damage to the equipment.